There is an app called Notebooks (http://www.notebooksapp.com/), which has basically everything I need (Check the image bellow). Still, this app is not free, and I wonder if there is a similar free app for windows 10.
The functionality I need is:
Notes organized in a tree, like it is shown in the image, you can organize your notes so that they belong to a specific category.
Keep it simple, I just need to writte plain text symbols, nothing more complicated. Pasting an image is usefull but not a must.
Thank you very much!